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The HIV/AIDS Pandemic: Advances Made and Challenges Ahead

This article discusses the progression of the HIV/AIDS pandemic, including the common characteristics, global impact, and challenges in developing a vaccine. It also explores the use of antiretroviral therapy and the potential of HIV-neutralizing monoclonal antibodies for prevention.

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The HIV/AIDS Pandemic: Advances Made and Challenges Ahead

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  1. The HIV/AIDS Pandemic: Advances Made and Challenges Ahead David D. Ho, M.D. Aaron Diamond AIDS Research Center, The Rockefeller University

  2. Los Angeles, 1981: tip of the iceberg – acquired immunodeficiency syndrome (AIDS) Common characteristics: gay men with marked depletion of CD4 T cells

  3. Homosexual men Female sex partners Injection drug users Blood transfusion recipients Hemophiliacs treated with factor VIII Children born to infected women CDC: Groups at risk for AIDS Sex Blood Mother to child

  4. 1983: detection of the causative agent – human immunodeficiency virus (HIV) F. Barre-Sinoussi & L. Montagnier

  5. The Global HIV Pandemic: 25 million dead and 35 million living The epidemic rages on with 2.5 million new infections per year

  6. Leading causes of death in Africa, 2000 22.6 25.0 20.0 15.0 % of Total 10.1 9.1 10.0 6.7 5.5 4.3 3.6 3.1 2.9 2.3 5.0 0.0 HIV/AIDS Malaria Perinatal conditions TB Cerebro- vascular disease Measles Lower respiratory infections Diarrheal disease Ischemic heart disease Maternal conditions

  7. 30 25 20 15 10 5 0 ‘91 ‘92 ‘93 ‘94 ‘95 ‘96 ‘97 ‘98 ‘99 ‘01 HIV prevalence among pregnant women in South Africa, 1990 to 2001 HIV prevalence (%) ‘90 ‘00

  8. Orphans in Sub-Saharan Africa: >12 million

  9. HIV-1: the causative agent of AIDS

  10. HIV-1 genomic organization

  11. HIV-1 life cycle and cellular factors that facilitate or restrict virus replication Tetherin (Vpu) CD4, CCR5, CXCR4 Tsg101, ALIX, ESCRT TRIM5α Why? APOBEC3G (Vif) P-TEFb LEDGF

  12. HIV-1 life cycle and antiretroviral drugs entry inhibitors protease inhibitors RT inhibitors Integrase inhibitors

  13. HIV-1 replication dynamics Duration: 1 d Cell t1/2: 0.7 d Virus t1/2: 30 min Virus production: 1010 to 1012 Darwinian evolution fast forward: >107 mutants per day: treat hard Heightened (4-6-fold) turnover of CD4 T-cells: treat early

  14. Sustained reduction of viral load by combination antiviral therapy

  15. Decline in AIDS mortality in the U.S. with the use of combination antiretroviral therapy since 1995 850,000 450,000 New AIDS cases Death 750,000 350,000 People living With AIDS 650,000 300,000 550,000 250,000 No. of cases and no. of deaths 450,000 No. of persons living with AIDS 200,000 350,000 150,000 250,000 100,000 150,000 50,000 5,000 0 0 1986 1988 1990 1992 1994 1996 1998 2000 2002 Year

  16. Social injustice: U.S. vs. Africa 1. The delivery of drugs and services to the developing world 2. The importance of prevention: education and vaccine

  17. No protective vaccine available No protective vaccine in the foreseeable future Where are we in HIV vaccine development?

  18. Difficulties in developing an HIV vaccine • During the natural course of HIV infection, the virus is seldom (<1%) well controlled by the immune system • Superinfection has been well documented • HIV is extremely plastic and rapidly escapes from immune recognition • HIV is relatively resistant to antibody neutralization

  19. Features of gp120 that preclude the efficient neutralization of HIV by antibodies Variable loops Glycosylation Entropic forces Chen et al. Nature, 433: 834, 2005.

  20. Notable HIV-neutralizing monoclonal antibodies b12: CD4-binding site on gp120 2G12: carbohydrate on gp120 2F5, 4E10: membrane-proximal region of gp41 PG9: conformational epitope on gp120 (Science, 2009) VRC01: CD4-binding site on gp120 (Science, 2010) PRO140: anti-CCR5 (anti-co-receptor) Ibalizumab: anti-CD4 (anti-receptor)

  21. Pre-exposure prophylaxis (PrEP) with HIV-neutralizing monoclonal antibodies If we are unable to induce neutralizing antibodies in vivo, why not produce them ex vivo for passive administration? And turn a heretofore intractable basic discovery problem into a more tangible engineering challenge.

  22. PrEP with tenofovir +/- emtricitabine has gained traction

  23. Concerns about daily oral PrEP • Adherence difficulty of a daily drug regimen in a healthy person • Potential long-term side effects of the drug(s) • Tenofovir +/- emtricitabine form the cornerstone of frontline ARV therapy Ideal PrEP agent -Infrequently administered -No side effects -No overlap with current therapies

  24. Ibalizumab: HIV-neutralizing mAb directed to domain 2 of human CD4 (5A8, TNX-355)

  25. Structure of ibalizumab Fab bound to 2-domain CD4 (2.2Å) Freeman et al, Structure, in press

  26. Contact sites between ibalizumab and CD4

  27. Superimposition of known structures of ibalizumab Fab, CD4, and gp120 core

  28. Breadth and potency of ibalizumab (MPI and IC50) against a panel of 118 HIV clones

  29. Ibalizumab is active and safe in vivo in humans Gates Foundation support to explore its use for PrEP

  30. Superimposition of known structures of ibalizumab Fab, CD4, MHC II-TCR,

  31. Ibalizumab as PrEP Moving toward proof of principle with the current form: Phase 1 study in healthy volunteers Passive protection against SIV challenge in macaques Making a better ibalizumab: Improve route Improve stability Improve affinity Improve PK Improve breadth Ultimate goal: Decrease dose to <10 mg Decrease frequency to 2 months Decrease cost

  32. Ibalizumab PK in monkeys: SC versus IV

  33. Making a better ibalizumab “Affinity maturation” Change IgG4 to IgG1-LALA Modify Fc to bind FcRn better Sustained release formulation

  34. Improving the stability of ibalizumab

  35. “In vitro affinity maturation” to select higher affinity variants

  36. Higher affinity variants of ibalizumab selected from CDR1H mutants

  37. Improving ibalizumab breadth by attacking a second site m36 PG9, VRC01

  38. m36 A fusion construct attacking CD4 and gp120 simultaneously iMab-m36

  39. Fusion with m36 broadens the breadth of ibalizumab iMab-S virusesiMab-R viruses

  40. iMab [1.6g/ml] iMab-m36 [1.6g/ml] Viruses iMab-m36 is active against ibalizumab-resistant viruses

  41. Other fusion constructs attacking both CD4 and gp120 or VRC01-scFv or VRC01-iMab

  42. VRC01 fusion also increases the breadth of ibalizumab III iMab

  43. Our ultimate goal To create improved variants of ibalizumab and other HIV-neutralizing monoclonal antibodies that are potent, broad, and could be given in low doses SC once every 2 months. It has not escaped us that such improved biologics could also be used, especially in combination, to change the paradigm of HIV therapy from daily to monthly regimens.

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